| 10:20 |
| Expand |
|---|
| title | Poster introductions (4 min. 1 slide each) |
|---|
|
| Div |
|---|
| Jake Bland (University of Reading, UK)
| Expand |
|---|
| title | UTLS humidity biases during NAWDEX |
|---|
|
| Div |
|---|
| Jake Bland1, Suzanne Gray1, John Methven1, Richard Forbes2 1University of Reading, UK
2ECMWF, UK Lower stratospheric moisture influences Rossby wave evolution through radiative induced temperature changes. Therefore it is expected that misrepresentation of moisture in models leads to forecast errors, which may propagate downstream and affect future system development. That the IFS exhibits a large moist bias in the lower stratosphere and an associated temperature bias is known, but the causes of this, and the impact on cyclone evolution are not. Work has been done to characterise these biases and investigate their behaviour in different conditions through comparisons of operational model data to radiosonde observations. This will be used to inform modelling studies to further investigate these biases in the IFS and their influence on cyclone development. |
|
Guokun Dai (Fudan University, Yun Chen (National Meteorological Center of China)
| Expand |
|---|
| title | Arctic influence Impact of Moist progress on the predictability of the cold surge occurred in China during January 2016Short-term Forecast of Rainfall Brought by Yagi to China in 2018 |
|---|
|
| Div |
|---|
| Guokun Dai Fudan University, China An extreme cold event occurred during 21-25 January 2016, which affected most areas in China, especially eastern China. Arctic influence on the predictability of the extreme cold event has been investigated with OpenIFS model. First, control experiments with different initial conditions are conducted and results show that integration with ERA-Interim reanalysis initial conditions performs better than that with ERA operational analysis. Diagnostic analyses have found that integration with ERA-Interim initial conditions has a better forecast of the Ural Blocking and Siberian High, which are crucial for the extreme cold event prediction. Subsequently, sensitive experiments are conducted to verify the influence of Arctic initial conditions on the predictability of the extreme cold event. Integrations with hybrid initial conditions, which remove the Arctic analysis errors from the ERA operational initial conditions, show an improved forecast skill of the cold event. Further investigations reveal that a more accurate Arctic initial condition can result in a better prediction of Ural Blocking and Siberian High, so that the forecast skill of the cold event improves. |
|
Mokhliss El-azaar (E HTP, Morocco) | Expand |
|---|
| | title | A coupled shallow and deep convection closure in OpenIFS |
|---|
| | Div |
|---|
| Noureddine Semane1, Siham Sbii2, Hannachi Abdel3, Mokhliss El-azaar1, Yamna Ghabbar1 1EHTP, Morocco
2Moroccan Meteorological Service
3University of Stockholm, Sweden The conventional convective available potential energy (CAPE) closure is based on the balance between the rate of CAPE change due to large-scale forcing and that due to deep convection, which is valid particularly for long time scales. Nonequilibrium convection, which is prominent at subdiurnal timescales, is well covered, however, when the CAPE closure incorporates the rate of CAPE change due to boundary layer forcing yielding nonequilibrium convection closure. This closure consists of subtracting from the total mass flux a fraction of the shallow cumulus contribution that is supposed to approximately balance the boundary layer forcing. The latter is newly parametrized here based on the moist static energy budget taking into account the enthalpy radiative tendency in the shallow convection layer. |
Federico Serva (CNR-ISMAR, Italy) | Expand |
|---|
| title | The stratospheric dynamics simulated by the OpenIFS model |
|---|
| | Div |
|---|
| Federico Serva CNR-ISMAR, Italy The variability in the stratosphere is coupled with surface climate and weather, and in recent years, many studies highlighted the need of a well-resolved stratosphere in numerical models, in order to improve their results. Including stratospheric processes in climate models is however computationally expensive, and also many phenomena are very sensitive to the models' resolution and parameterized physics. Since the stratosphere is an important element of the long-term climate variability, it is important that its realistic representation is included in climate models, supported by extensive testing and sensitivity studies. We present the objectives of a recently started ECMWF Special Project, aiming to gain a better understanding of stratospheric dynamical processes in the OpenIFS' model, and their sensitivity to the model configuration. The outcomes of this work could be beneficial for the future inclusion of the OpenIFS model in a comprehensive Earth System Model. |
Lorenzo Silvestri (CIRIAF-CRC, University of Perugia, Italy) | Expand |
|---|
| title | OpenIFS Held-Suarez test: an educational application of the statistical equilibrium concept |
|---|
| Yun Chen, Jun Xu National Meteorological Center of China Yagi, the No. 14 typhoon that made its landfall in Zhejiang province on August 12, 2018, brought severe rainstorms to northern China on August 13 and 14, with its maximum daily precipitation over 300mm and its maximum hourly precipitation over 120mm. This event, however, was not well forecasted. The 24-h rain-area forecast, made based on forecasts of ECWMF IFS, was west to the observation by more than 100 kilometers. With an analysis on the circulation and precipitation fields, we found that this bias in heavy-rain region forecast was caused by both biases in typhoon track and precipitation pattern. The forecast of typhoon track was sensitive to initial fields and moist progress. Our sensitivity analysis of ECWMF ensemble forecast revealed that subtropical high being north to the observation and a weaker-than-observation upper trough near Baikal in initial field will lead to a track forecast west to the observation. Without these two biases, only in Member 18 of ECWMF ensemble forecast, the forecast of heavy rainfall region was closer to the observation. The bias in the precipitation pattern was related to the bias in simulating MCS. The rain bands developed in an environment characterized by high relative humidity, high freezing level, and moderate CAPE, favorable for high precipitation efficiency. Near the periphery of typhoon, the boundary layer was highly humid and warm. Easterly wind speed convergence within the boundary layer triggered and maintained MCS, which manifested a train effect, leading to heavy rainfall. However, ECWMF did not describe MCS well and therefore predicted much more precipitation in the north and west of typhoon while underestimated the MCS precipitation near the east. This, in turn, led to biases in the low-level wind through excessive latent heat release and further led to a bias in the track forecast. In conclusion, this bias of landfall typhoon precipitation forecast was caused by both biases in initial errors and moist progress. But which one was more important and interaction between them need to do further research work. |
|
Guokun Dai (Fudan University, China) | Expand |
|---|
| title | Arctic influence on the predictability of the cold surge occurred in China during January 2016 |
|---|
|
| Div |
|---|
| Guokun Dai Fudan University, China An extreme cold event occurred during 21-25 January 2016, which affected most areas in China, especially eastern China. Arctic influence on the predictability of the extreme cold event has been investigated with OpenIFS model. First, control experiments with different initial conditions are conducted and results show that integration with ERA-Interim reanalysis initial conditions performs better than that with ERA operational analysis. Diagnostic analyses have found that integration with ERA-Interim initial conditions has a better forecast of the Ural Blocking and Siberian High, which are crucial for the extreme cold event prediction. Subsequently, sensitive experiments are conducted to verify the influence of Arctic initial conditions on the predictability of the extreme cold event. Integrations with hybrid initial conditions, which remove the Arctic analysis errors from the ERA operational initial conditions, show an improved forecast skill of the cold event. Further investigations reveal that a more accurate Arctic initial condition can result in a better prediction of Ural Blocking and Siberian High, so that the forecast skill of the cold event improves. |
|
Mokhliss El-azaar (E HTP, Morocco) | Expand |
|---|
| title | A coupled shallow and deep convection closure in OpenIFS |
|---|
|
| Div |
|---|
| Noureddine Semane1, Siham Sbii2, Hannachi Abdel3, Mokhliss El-azaar1, Yamna Ghabbar1 1EHTP, Morocco
2Moroccan Meteorological Service
3University of Stockholm, Sweden The conventional convective available potential energy (CAPE) closure is based on the balance between the rate of CAPE change due to large-scale forcing and that due to deep convection, which is valid particularly for long time scales. Nonequilibrium convection, which is prominent at subdiurnal timescales, is well covered, however, when the CAPE closure incorporates the rate of CAPE change due to boundary layer forcing yielding nonequilibrium convection closure. This closure consists of subtracting from the total mass flux a fraction of the shallow cumulus contribution that is supposed to approximately balance the boundary layer forcing. The latter is newly parametrized here based on the moist static energy budget taking into account the enthalpy radiative tendency in the shallow convection layer. |
|
Ying Li (Chinese Academy of Meteorological Sciences) | Expand |
|---|
| title | An ensemble analysis on abrupt north turning of typhoon Meranti (2010) under the influence of an upper tropospheric cold low |
|---|
|
| Div |
|---|
| Ying Li Chinese Academy of Meteorological Sciences The sudden change of typhoon track is one of challenges in typhoon forecast. Typhoon Meranti (2010) experienced an abrupt northward turning when it moved westward to the south of Taiwan Island. Ensemble forecast outputs from the European Medium Range Weather Forecasts (ECMWF) presented a large random for the north turning. The good group consisting of 8 members which predicted the abrupt northward turning well is compared to the poor group including 8 members which did not predict the unusual track, to investigate the main influence factors on the northward turning of typhoon Meranti. Results show that: 1) An upper tropospheric cold low (UTCL) cut from tropical upper-tropospheric trough (TUTT) is an important factor impacting the typhoon track change. The abrupt northward turning of typhoon Meranti is related to the coupling between Meranti and the nearby UTCL in north-south direction. 2) The UTCL can change the upper tropospheric environmental flow around the typhoon, and then influence the typhoon steering flow. When the UTCL moved to the north of Meranti, the southerly component of steering flow for typhoon movement was enhanced, which is helpful to the movement northward of Meranti. 3) The northward turning of Meranti is also associated with the vertical structure of UTCL. The UTCL with wide and deep cyclonic circulation in vertical direction is more favorable to the track change. 4) The diagnostic analysis on the potential vorticity tendency equation showed that, under the coupling between Meranti and UTCL in north-south direction, the potential vorticity horizontal advection in the north of typhoon is strengthened, which is helpful for the northward movement of Meranti. And the asymmetric wind advection of potential vorticity has a major contribution to the north track under the influence of UTCL. |
|
Federico Serva (CNR-ISMAR, Italy) | Expand |
|---|
| title | The stratospheric dynamics simulated by the OpenIFS model |
|---|
|
| Div |
|---|
| Lorenzo Silvestri, Paolina Bongioannini Cerlini CIRIAF-CRC, University of Perugia, Italy The Held Suarez paper (1994) proposed a solution to the problem of testing the models dynamical core results given the fact that there are no exact solutions of the primitive equations with realistic forcing. The OpenIFS model has among other tests of the code, the Held Suarez case where physics parametrization schemes of the full model are replaced by prescribed forcing and dissipation. The radiative equilibrium solution that is found, simulates a circulation that is reasonably realistic in many aspects without the burden of physical parametrizations. During classes the Open-IFS model gives the students the possibility to run this case and one other test that start from the same idea but with different initial equilibrium temperature, modified by Williamson et al. (1998) to include stratospheric structures so to give increasing temperature in the Tropics, where the radiative equilibrium solution produces bias using different numerical schemes of the GCM that was tested. The conceptual framework of the Held-Suarez case with the various options, allows to introduce the idea of running a test to understand the theoretical dynamics and the way it is build within the OpenIFS code, and to understand how the initial conditions can change the model equilibrium. The equilibrium that is found can be then studied statistically using the run with different initial conditions in order to evaluate its sensitivity and internal variability. This case has been run at University of Perugia to teach applications of the general circulation primitive equations and to train the teacher and PhD students in configuring and running in a local environment the 3D version of the OpenIFS model. References: Held, I. M., and M. J. Suarez, 1994: A proposal for the intercomparison
of the dynamical cores of atmospheric general circulation models. Bull. Amer. Meteor. Soc., 75, 1825-1830. Williamson D. L., J. G. Olson, B. A Boville, 1998): A comparison of semi-Lagrangian and Eulerian tropical climate simulations. Mon. Wea. Rev. 126, 1001-1012del. |
Irina Statnaia (University of Helsinki, Finnish Meteorological Institute) | Expand |
|---|
| title | OpenIFS simulations for SSW 2018 |
|---|
|
| Div |
|---|
| Irina Statnaia1,2, Alexey Karpechko2, Victoria Sinclair1, Heikki Järvinen1 1University of Helsinki, Finland
2Finnish Meteorological Institute In mid-latitudes, and also in Europe, forecasts typically lose their skill after about 10 days. This occurs due to chaotic nature of weather processes. In turn, weather predictability is variable and there are situations when weather becomes more predictable. For the mid-latitudes during boreal winter a major source of sub-seasonal predictability is variability of the stratospheric polar vortex. Stratospheric circulation affects development and growth of cyclones and storm tracks beneath. In extreme case, when stratospheric polar vortex breaks down in an event called Sudden Stratospheric Warming (SSW), tropospheric storm tracks are typically shifted southward making northern and central Europe affected by cold Arctic air masses. Ability to predict SSW can extend weather predictability beyond 2 weeks. In this study, we investigate the SSW case that took place on 12 February 2018 (SSW2018), its predictability and surface climate impacts by using the OpenIFS model, initialised with different model setups (lead time, resolution, timestep). In order to better understand the sources of uncertainties, to detect model biases and investigate whether there are windows of opportunity within which the model may be more skilful, we make sensitivity experiments with different parameterization schemes. The results obtained with the OpenIFS forecast data are compared with the ECMWF’s reanalysis ERA-Interim (ERA-I) and ERA-5. The analysis of the OpenIFS forecasts obtained within different sensitivity experiments shows the impact of orographic and non-orographic gravity wave drag, which affects the lead-time of a successful forecast and strength of the SSW2018 event. Hence, tuning of the parameterisation schemes can contribute to enhanced predictability, but the model performance should also be studied beyond a small number of case studies of individual extreme events. |
|
Lauri Tuppi (University of Helsinki, Finland) Federico Serva CNR-ISMAR, Italy The variability in the stratosphere is coupled with surface climate and weather, and in recent years, many studies highlighted the need of a well-resolved stratosphere in numerical models, in order to improve their results. Including stratospheric processes in climate models is however computationally expensive, and also many phenomena are very sensitive to the models' resolution and parameterized physics. Since the stratosphere is an important element of the long-term climate variability, it is important that its realistic representation is included in climate models, supported by extensive testing and sensitivity studies. We present the objectives of a recently started ECMWF Special Project, aiming to gain a better understanding of stratospheric dynamical processes in the OpenIFS' model, and their sensitivity to the model configuration. The outcomes of this work could be beneficial for the future inclusion of the OpenIFS model in a comprehensive Earth System Model. |
|
Lorenzo Silvestri (CIRIAF-CRC, University of Perugia, Italy) | Expand |
|---|
| title | OpenIFS Held-Suarez test: an educational application of the statistical equilibrium concept |
|---|
|
| Div |
|---|
| Lorenzo Silvestri, Paolina Bongioannini Cerlini CIRIAF-CRC, University of Perugia, Italy The Held Suarez paper (1994) proposed a solution to the problem of testing the models dynamical core results given the fact that there are no exact solutions of the primitive equations with realistic forcing. The OpenIFS model has among other tests of the code, the Held Suarez case where physics parametrization schemes of the full model are replaced by prescribed forcing and dissipation. The radiative equilibrium solution that is found, simulates a circulation that is reasonably realistic in many aspects without the burden of physical parametrizations. During classes the Open-IFS model gives the students the possibility to run this case and one other test that start from the same idea but with different initial equilibrium temperature, modified by Williamson et al. (1998) to include stratospheric structures so to give increasing temperature in the Tropics, where the radiative equilibrium solution produces bias using different numerical schemes of the GCM that was tested. The conceptual framework of the Held-Suarez case with the various options, allows to introduce the idea of running a test to understand the theoretical dynamics and the way it is build within the OpenIFS code, and to understand how the initial conditions can change the model equilibrium. The equilibrium that is found can be then studied statistically using the run with different initial conditions in order to evaluate its sensitivity and internal variability. This case has been run at University of Perugia to teach applications of the general circulation primitive equations and to train the teacher and PhD students in configuring and running in a local environment the 3D version of the OpenIFS model. References: Held, I. M., and M. J. Suarez, 1994: A proposal for the intercomparison
of the dynamical cores of atmospheric general circulation models. Bull. Amer. Meteor. Soc., 75, 1825-1830. Williamson D. L., J. G. Olson, B. A Boville, 1998): A comparison of semi-Lagrangian and Eulerian tropical climate simulations. Mon. Wea. Rev. 126, 1001-1012del. |
|
Irina Statnaia (University of Helsinki, Finnish Meteorological Institute) | Expand |
|---|
| title | OpenIFS simulations for SSW 2018 |
|---|
|
| Div |
|---|
| Irina Statnaia1,2, Alexey Karpechko2, Victoria Sinclair1, Heikki Järvinen1 1University of Helsinki, Finland
2Finnish Meteorological Institute In mid-latitudes, and also in Europe, forecasts typically lose their skill after about 10 days. This occurs due to chaotic nature of weather processes. In turn, weather predictability is variable and there are situations when weather becomes more predictable. For the mid-latitudes during boreal winter a major source of sub-seasonal predictability is variability of the stratospheric polar vortex. Stratospheric circulation affects development and growth of cyclones and storm tracks beneath. In extreme case, when stratospheric polar vortex breaks down in an event called Sudden Stratospheric Warming (SSW), tropospheric storm tracks are typically shifted southward making northern and central Europe affected by cold Arctic air masses. Ability to predict SSW can extend weather predictability beyond 2 weeks. In this study, we investigate the SSW case that took place on 12 February 2018 (SSW2018), its predictability and surface climate impacts by using the OpenIFS model, initialised with different model setups (lead time, resolution, timestep). In order to better understand the sources of uncertainties, to detect model biases and investigate whether there are windows of opportunity within which the model may be more skilful, we make sensitivity experiments with different parameterization schemes. The results obtained with the OpenIFS forecast data are compared with the ECMWF’s reanalysis ERA-Interim (ERA-I) and ERA-5. The analysis of the OpenIFS forecasts obtained within different sensitivity experiments shows the impact of orographic and non-orographic gravity wave drag, which affects the lead-time of a successful forecast and strength of the SSW2018 event. Hence, tuning of the parameterisation schemes can contribute to enhanced predictability, but the model performance should also be studied beyond a small number of case studies of individual extreme events. |
|
Lauri Tuppi (University of Helsinki, Finland) | Expand |
|---|
| title | Algorithmic optimization of model closure parameters using ensemble forecasts |
|---|
|
| Div |
|---|
| Lauri Tuppi1, Madeleine Ekblom1, Pirkka Ollinaho2, Marko Laine2, Vladimir Shemyakin3, Heikki Järvinen1 1University of Helsinki, Finland
2Finnish Meteorological Institute
3Lappeenranta University of Technology, Finland
Algorithmic methods designed for tuning of numerical weather prediction (NWP) models are gaining popularity since manual tuning is a laborious task. Automation of the tuning process would save the model developers’ time. In this study, we will study the performance of two algorithms in a realistic ensemble prediction system using OpenIFS. The methods are the original distribution based Ensemble Prediction and Parameter Estimation System (EPPES) (Järvinen et al. 2012, Laine et al. 2012) and its population based variant Differential Evolution EPPES (DE-EPPES) (Shemyakin and Haario 2018). A necessary prerequisite for successful optimization is a successful convergence test. Convergence test is an optimization experiment where the reference state (usually analysis) has been replaced with a control forecast with known fixed parameters. As the truth is known, one can see from the results when the convergence is successful, and the algorithm is working correctly. The convergence tests begin with slightly wrong parameter values and too large uncertainty. The target is to find those known parameter values of the control forecast. We chose to use two parameters from the convection scheme of OpenIFS in our convergence tests. We explore different experimental set-ups (ensemble size, forecast length, different algorithms) and their effect on the convergence of the parameters to find the most efficient model tuning set-up. Järvinen, H. et al., 2012. http://dx.doi.org/10.1002/qj.923.
Laine, M. et al., 2012. http://dx.doi.org/10.1002/qj.922.
Shemyakin, V. & Haario, H., 2018. https://doi.org/10.1007/s11071-018-4239-5. |
|
Zuowei Xie (Institute of Atmospheric Physics, Chinese Academy of Sciences) | Expand |
|---|
| title | The Structure and Large-scale Organization of Extreme Precipitation Events over Indochina Peninsula and Southern China |
|---|
| | Expand |
|---|
| title | Algorithmic optimization of model closure parameters using ensemble forecasts |
|---|
|
| Div |
|---|
| Zuowei Xie Institute of Atmospheric Physics, Chinese Academy of Sciences Extreme precipitation events (EPEs) occurring over Indochina Peninsula and southern China (INCSC) are studied through a systematic identification and documentation of their local synoptic structures, associated large-scale meteorological patterns (LMPs). Focusing on the wet season (April–October) for 1951‒2015, a self-organization map identifies six EPE patterns, respectively characterized by increased precipitation anomalies over eastern Indochina, central INCSC, southeastern southern China, western INCSC, northwestern INCSC and northern southern China respectively. The leading three groups are associated with moisture flux from Indian Ocean and South China Sea, while the rest three groups are characterized by moisture flux mainly from Indian Ocean. In the mid-troposphere, the first and sixth groups features a dipole anomalous circulation over southern Asian and Lake Baikal with Rossby wave flux from the tropical region, while the other groups are associated with various Rossby wave trains over the mid-latitude Eurasia. There is a significant long-term upward trend in the total number of EPEs, which is contributed from clusters 1, 4 and 6. |
|
Jun Xu (National Meteorological Center of China) | Expand |
|---|
| title | Impact of Moist Convective Progress on Extreme Frontal Rainstorm Forecast Using ECMWF IFS |
|---|
|
| Div |
|---|
| Jun Xu National Meteorological Center of China Forecast of frontal rainstorm remains a big challenge for forecasters and NWP when moist convective processes are considered, although the influencing synoptic systems are well predicted. Using ECMWF IFS forecast, we selected a case of extreme frontal rainstorm with obvious convection attacked North China on April 21 2018 to study the predictability and causes of biases. Influenced by the heat and moisture transport brought by extremely strong low-level jet, warm sector rain band, narrow rain-band and wide rain-band were included in the frontal precipitation, which was consist with the typical frontal precipitation pattern proposed by Houze. The narrow rain-band was the center of precipitation; it was featured by significant moist convection and long-lasting precipitation. Though 24-h accumulated precipitation threat score in 36-h forecast reached 0.36, ECMWF IFS underestimated the narrow rain-band precipitation while overestimated the grid-scale precipitation at the back of front. The excessive low-level latent heat feedback associated with the excessive grid-scale precipitation in turn led to stronger and slowly-moving synoptic vortex systems in the model, resulting in significant large-scale bias within the 36-h forecast. Predictability research showed that initial errors were distributed from meso-scale to synoptic scale. Before the onset of the main moist convection, the errors had been concentrated in waves with length of 500-1000km. Besides deficiency of convective parameter, forecast of a weaker synoptic scale wind speed fluctuation and a lower surface temperature could also lead to the underestimation of moist convection and overestimation of grid-scale precipitation. After the 15-hour-long moist process, the errors concentrated at scales larger than 1000km. Results also revealed that the rapid error growth period was in keeping with the moist convective process. In conclusion, deficiency in moist convection could lead to error growth above synoptic scale in short-term forecast, and limit ECMWF IFS predictability Lauri Tuppi1, Madeleine Ekblom1, Pirkka Ollinaho2, Marko Laine2, Vladimir Shemyakin3, Heikki Järvinen1 1University of Helsinki, Finland
2Finnish Meteorological Institute
3Lappeenranta University of Technology, Finland
Algorithmic methods designed for tuning of numerical weather prediction (NWP) models are gaining popularity since manual tuning is a laborious task. Automation of the tuning process would save the model developers’ time. In this study, we will study the performance of two algorithms in a realistic ensemble prediction system using OpenIFS. The methods are the original distribution based Ensemble Prediction and Parameter Estimation System (EPPES) (Järvinen et al. 2012, Laine et al. 2012) and its population based variant Differential Evolution EPPES (DE-EPPES) (Shemyakin and Haario 2018). A necessary prerequisite for successful optimization is a successful convergence test. Convergence test is an optimization experiment where the reference state (usually analysis) has been replaced with a control forecast with known fixed parameters. As the truth is known, one can see from the results when the convergence is successful, and the algorithm is working correctly. The convergence tests begin with slightly wrong parameter values and too large uncertainty. The target is to find those known parameter values of the control forecast. We chose to use two parameters from the convection scheme of OpenIFS in our convergence tests. We explore different experimental set-ups (ensemble size, forecast length, different algorithms) and their effect on the convergence of the parameters to find the most efficient model tuning set-up. Järvinen, H. et al., 2012. http://dx.doi.org/10.1002/qj.923.
Laine, M. et al., 2012. http://dx.doi.org/10.1002/qj.922.
Shemyakin, V. & Haario, H., 2018. https://doi.org/10.1007/s11071-018-4239-5. |
|
|
| 10:20 | Terhi Laurila (Finnish Meteorological Institute) | Expand |
|---|
| title | Transition of Hurricane Debby (1982) and Its Re-Development into an Intense Windstorm over Finland |
|---|
|
| Div |
|---|
| Terhi Laurila1, Victoria Sinclair2, Hilppa Gregow1 1Finnish Meteorological Institute
2University of Helsinki, Finland On 22 September 1982, an intense windstorm Mauri led to extensive wind damage in northern Finland. Mauri was potentially related to the extratropical transition of Hurricane Debby which is an uncommon origin for a windstorm in Fenno-Scandinavia. In this study, we analyze the synoptic-dynamic evolution of Mauri to investigate the role of Debby in its development, and we examine the physical reasons for strong wind gusts over Finland. A brief synoptic overview was conducted based on ERA-Interim and a more detailed analysis was performed based on multiple OpenIFS simulations with different initialization times. We found that Debby did not immediately re-intensify when it reached the mid-latitudes due to lack of upper-level support. However, ex-Debby was able to self-maintain itself as a diabatic Rossby wave while traveling rapidly across the Atlantic. Near the UK, ex-Debby rapidly re-intensified when it interacted with an upper-level potential vorticity anomaly of another extratropical cyclone. This intensification was not captured in OpenIFS simulations initialized on 17 and 19 September since the phasing of upper and lower-level anomalies was incorrectly simulated. In the simulation from 21 September, the re-intensification of ex-Debby was captured and the wind gusts over northern Finland were stronger than in the other simulations. Strong pressure gradients caused the strong wind speeds and the wind gusts were further enhanced behind the cold front due to turbulent mixing and in the warm sector due to convectively driven downdrafts. In conclusion, Mauri was connected to Hurricane Debby but the interaction with another extratropical cyclone over the UK was critical for ex-Debby to re-develop into an intense windstorm over Finland. |
|
| Mika Rantanen (University of Helsinki, Finland) | Expand |
|---|
| title | The extratropical transition of Hurricane Ophelia (2017) as diagnosed with a generalized omega equation and vorticity equation |
|---|
|
| Div |
|---|
| Mika Rantanen, Jouni Räisänen, Victoria Sinclair, Heikki Järvinen University of Helsinki, Finland Hurricane Ophelia was a category 3 hurricane which underwent an extratropical transition and made landfall in Europe as an exceptionally strong post-tropical cyclone in October 2017. In Ireland, for instance, Ophelia was the worst storm in 50 years and resulted in significant damage and loss of life. In this study, the different physical processes affecting Ophelia’s transformation from a hurricane to a mid-latitude cyclone are studied. For this purpose, we have developed software which uses OpenIFS model output and a system consisting of a generalized omega equation and vorticity equation. By using these two equations, the atmospheric vertical motion and vorticity tendency are separated into the contributions from different physical processes: vorticity advection, thermal advection, friction, diabatic heating, and the imbalance between the temperature and vorticity tendencies. Vorticity advection, which is often considered an important forcing for the development of mid-latitude cyclones, is shown to play a small role in the re-intensification of Ophelia as an extratropical storm. This is because the effects of divergent and non-divergent components of vorticity advection mainly cancelled each other out, resulting in a net effect close to zero. However, our results show that diabatic heating was the dominate forcing in both the tropical and extratropical phases of Ophelia. Furthermore, we calculated in more detail the diabatic heating contributions from different model parameterizations. We find that the temperature tendency due to the convection scheme was the dominant forcing for vorticity tendency during the hurricane phase, but as Ophelia transformed into a mid-latitude cyclone, the microphysics temperature tendency gradually increased becoming the dominant forcing once the transition was complete. |
|
| Group presentations (max. 20 min. each), discussion |